The field of the invention is optical fibers.
Optical fibers are used to direct light of various light frequencies along an optically transparent material. They are typically comprised of a core, cladding and buffer or coating. The core, is at the core of the fiber and like the other two constituents runs parallel to the longitudinal axis of the fiber. The cladding surrounds the sides of the core and the buffer or coating in turn surrounds the sides of the cladding. The buffer acts as a mechanical and chemical protective external layer for the cladding and core. The core acts together with the cladding to direct the radiation down the longitudinal axis of the core. This is possible because the core and cladding are made of materials that allow the light wave to move slightly faster through the cladding than the core. This has the effect of bending the radiation that is incident on the cladding to move into the core, thus projecting the radiation down the longitudinal axis of the core. This redirection is accomplished with little loss of energy and hence the fiber can deliver optical energy or thermal-optical energy for considerable distances.
Sometimes however it is desirable to have the optical energy leak out the sides of the optical fiber at selected sites along the fiber, rather than tapping the energy that projects out of the end of the fiber that is distal to the laser or other device that delivers the energy into the fiber at the proximal end.
The advantage of doing so might be to distribute the output over a relatively large area compared to that emerging from the distal end of the optical fiber. This would permit a vast number of detectors or optical fiber receivers to receive the energy and information and if required retransmit it. These detectors or rerouting optical fibers could be coupled with filters, well known to the art that would permit the tapping of specific frequencies from the leaking fiber.
The leakage from relatively large areas along the side of the fiber could be also be used to project photo-thermal energy to the area external to the fiber. This might be used to heat the inside of SMA tubes to either effect shape recovery as for example taught by Unsworth and Waram in U.S. Pat. No. 5,846,247 or to effect a stiffening of superlastic SMA tubes as taught by Unsworth, Waram and Adelman in U.S. Pat. No. 5,904,657. The side of the optical fiber might be treated around its entire circumference or around only a part of it. This would permit the selective projection onto parts of the interior of the tubes without recourse to mirroring or beveling the distal end of the core of the fiber. By causing the sides of the optical fiber to leak, a larger area of the tube or other material can be heated or treated with photo-optical or photo-thermal energy. This would be an advantage where a guidewire made of superlastic SMA could be heated along a relatively long length causing it to stiffen when heated and thus assisting the surgeon in advancing the wire through an occlusion. This heated SMA tube could also be used for ablative surgery, used to treat the walls of the heart for prevention of atrial fibrillation. Another use for an optical fiber thus treated would be for triggering light activated drugs. The larger area of projection would permit the site specific activation of a larger site which would speed the operation and avoid the necessity of relocating the optical fiber and catheter.
Alternatively, the leaks could be from the side of the fiber, that were of such a size that only particular frequencies could leak through the xe2x80x9cholesxe2x80x9d in the walls of the cladding. xe2x80x9cHolesxe2x80x9d in the cladding would permit passage of those frequencies that have wavelengths less than or equal to approximately twice the size of the hole with progressively less permissibility up to approximately four times the size of the xe2x80x9cholexe2x80x9d. xe2x80x9cHolesxe2x80x9d, need not be actual holes in the cladding, but include any treated area of the same size, that causes the optical energy of that frequency not to refract back into the core in the manner it does on the untreated portions of the cladding. Typically this would be effected by lowering the speed though which energy of a desired frequency can pass through the cladding at this treated area below or equal to that speed which it travels through the core; or conversely, by increasing the speed with which the energy passes through the core, at that treated point. A method for creating these xe2x80x9cholesxe2x80x9d will be described below. These xe2x80x9cholesxe2x80x9d can be arranged, with the smallest toward the proximal end of the fiber and the larger xe2x80x9cholesxe2x80x9d near the distal end, such that specific frequencies could be tapped in succession, much like a coal or gravel sorter used in mines and quarries. While some shorter frequencies that should exit the smaller xe2x80x9cholesxe2x80x9d, would inevitably pass by the smaller xe2x80x9cholesxe2x80x9d, and emerge out of the further distal larger xe2x80x9cholesxe2x80x9d, the output energy would be lower permitting selective filtering or setting the detector or detectors at the larger xe2x80x9cholesxe2x80x9d to detect only above a threshold set above that of the likely errant high frequency output. It should be noted that these xe2x80x9cholesxe2x80x9d need not be round, but can be of any convenient shape, so long as their dimensions act to filter out radiation of unwanted wave-lengths.
While brad gratings are used routinely in effecting some leakage from the side of the optical fiber, it is difficult to effect and generally allows for only very small areas of leakage. These gratings are created with masks that rapidly deteriorate when subjected to the imprinting laser light from a source external to the optical fiber that is being treated.
The method outlined in this invention includes the use of a laser that heats the cladding of the optical fiber in quick pulses that act to change the optical properties of the cladding sufficiently to leak at a predictable and even rate. The rapid application of pulses of heat followed by cooling periods is thought to alter the optical properties of the cladding or core or both and cause a leaking of energy from the core through the cladding to the space surrounding the fiber. When the buffer is left on the optical fiber and is burned away by the laser, the cladding may become contaminated or doped and thus its optical properties may deteriorate, thereby increasing the leaking of the photo energy from the core to the exterior of the optical fiber. This contamination or doping of the cladding by the application of the laser pulses in combination with the intimate presence of other chemicals makes possible the doping of specific parts of the cladding to permit specific frequencies of light to leak while maintaining the normal light transmitting properties for other frequencies. Such doping chemicals can be placed on the selected area of cladding (after the buffer has been removed) and the treating laser can then heat the cladding sufficiently to allow for the incorporation of the dopant into the cladding. These dopants that are frequency specific are well known to the art of photonics. Where the dopant is in vapor or plasma form, the procedure would of course need to be conducted in a suitable chamber. It should be noted that these methods work for polymer as well as glass cores, cladding and buffers or combinations of them.
Any treatment of the optical fiber than makes it leak will usually make it more brittle and susceptible to breakage if alter flexed, even if the buffer is reapplied. The method herein described includes a method for reducing breakage, but should breakage occur, maintains near normal light passage down the fiber.
The method of rendering the leaky fiber leaky is simple and inexpensive especially when the optical fibers are transmitting photo-thermal energy comprised largely of infrared. For example the use of an inexpensive engraving/cutting type xe2x80x9cX/Yxe2x80x9d moving platen laser station, such as the Trotec 25 watt xe2x80x9cSpeedyxe2x80x9d laser is ideal for creating large leaky sections on an optical fiber. While the buffer might for some applications be removed chemically prior to laser treatment, this is often not necessary as the laser heat removes the buffer as it treats the cladding and core or both below. Other dopants could as described above be placed in intimate contact with the part of the optical fiber to receive laser treatment.
The optical fiber can be placed on the work table and that part of the optical fiber that needs to leak can be treated by passing the laser beams in a series of parallel paths approximately normal to the longitudinal axis of the fiber. Such series of paths forming a treated patch along the optical fiber. The paths could of course be at other angles to the longitudinal axis, including parallel, or even crosshatched to vary the amount of light that is emitted. The angles and number of passes back and forth will be governed by the amount of light that is required to be emitted. Spots that create xe2x80x9cholesxe2x80x9d can also be imparted into the laser by short and pin-point pulses as the laser tracks across the optical fiber. The advantage of this method is that by varying the power of the laser, the pulse frequency and the speed with which is tracks across the fiber, the effect on the cladding can be varied and thus the amount of light emitted. By varying these factors, a patch of fiber can have a pattern of brighter and less bright emitting parts as required. The amount of light that is emitted from the side of the fiber will depend on the type of fiber chosen, the frequency or frequencies of light that travel along the fiber as well as the treatment options chosen. The treatment options chosen will initially be a matter of trial and error to match the operator""s requirements with the materials at hand.
As an example of a treatment of an optical fiber an optical fiber designed to carry photo-thermal energy (mainly infrared) can be easily be made leaky by using the Trotec xe2x80x9cSpeedyxe2x80x9d machine, or similar machine. In this case a very even output over an inch of the optical fiber was obtained. Other tests using slightly different parameters gave an even output over approximately four inches. Other methods have produced very short distances of leakyness, perhaps a quarter of an inch. Using the Totech machine (a machine of similar design could also be used), the tip of the optical fiber was made evenly leaky by passing the laser normal to the longitudinal axis of the optical fiber at the rate of approximately 9.2 inches per second, back and forth slightly wider a path than the width of the fiber, to ensure there are no parts of the fiber that do not get treated. The CO2 laser output was set at the full 25 watts at 1000 Hertz pulse rate. Each succeeding pass was separated by approximately 2,000 of an inch, giving approximately 500 passes of the laser, normal to the longitudinal axis of the fiber and evenly spaced over an inch along the longitudinal axis of the fiber. The separation between passes or the power or both can be varied from the first passes to the last to vary the leakage produced, or to compensate for the reduced power available to leak at the distal section of the fiber. This varied output can create patterns suitable for display or for reading bar codes or other printed matter. These parameters will of course require adjustment depending upon the optical fiber used and the frequency of energy traveling down the optical fiber. It is important that the power setting be such that the fiber is not cut. The best way to calibrate the power setting is to connect the optical fiber (or a test fiber in an array, if many are treated at once) to the laser with which it will actually be used. This way the output can be directly tested as the parameters are set, either visually or with instrumentation, and perhaps a feedback controller.
This method is fast and avoids the necessity of using expensive high frequency lasers and masks. This method also allows for hundreds of fibers to be lined up side by side and to be treated at once. In this case the truck travels across the entire array of fibers on each pass. The truck housing the laser courses back and forth normal to the longitudinal axes of the fibers along a traveling platen whose longitudinal axis is normal to the longitudinal axes of the fibers, the movable platen moving approximately parallel to the axes of the fibers.
In many cases the fiber can be treated on one side only, as the cladding and perhaps the core can be altered around part or all of its circumference by appropriately choosing the power, frequency, pulse rate, path separations, and speed of travel of the laser. In some cases only a part of the circumference needs to project light or leak in which case setting are chosen that will restrict the effect of the laser to the spot on which the laser actually projects its photo-thermal energy, usually lower power settings.
Such engraving/cutting laser systems can include a rotating tool that holds and rotates the optical fiber so that it rotates about its longitudinal axis, while the laser applies photo-thermal energy in the same manner as described above.
This type of laser can also form small patches, referred to above as xe2x80x9cholesxe2x80x9d, by pulsing on spots along the fiber rather than being turned on while the truck travels along the platen creating paths. These patches can be doped as described above, or simply heated by the treating laser. In the case where the xe2x80x9cholesxe2x80x9d are meant to selectively leak light of higher frequencies, a laser of higher frequency will be required and a platen having greater precision than the Trotec xe2x80x9cSpeedyxe2x80x9d machine.
Optical fibers can be directly attached to these xe2x80x9cholesxe2x80x9d by adhesives or fixtures, to route the photo-optical or photo-thermal energy traveling down the optical fiber to branch in many directions. The holes can also be connected directly to detectors to read the information contained in the energy emitted from the holes. A further possibility is to dope the holes as described above with materials that change their optical properties in the presence of another laser beam that turns on and off the spot by alternatively applying or not applying energy to that spot. The said changed optical properties would make the cladding behave normally when, for example, the light was not shone on the spot, but become a slower medium when the laser light was shone on the spot, causing the beam traveling down the optical fiber to leak through the cladding at that point. The treatment of the optical fiber described could thus act as a branching and switching network.
When the treatment is complete a transparent buffer may in certain circumstances be placed over the treated area to protect it from environmental degradation. If this is desirable, a clear silicone or other flexible polymer coating that shrinks when it sets may be for certain applications be useful. Once such acrylic polymer is available from Golden Artists Colors, regular gel medium. This material has been found to shrink which compresses the optical fiber when it sets. This has the advantage that if the optical fiber subsequently breaks, the compression both radially and longitudinally along the fiber acts to hold the broken fiber ends together and to minimize the loss of performance of the optical fiber. This treatment of the fiber is not of course limited to that part of the fiber subject to flexure. In the case where the fiber buffer need not transmit the leaking energy, non transmissive, polymers could be used. Provided they shrink and act to compress the optical fiber as described above.